The present invention relates to a method and a device for communication between a low potential level and a valve located at a high voltage potential level in a high voltage converter station. The valve has a plurality of valve units each having at least one semiconductor component of turn-on type and, for each semiconductor component, a first control unit located on a high voltage potential level and controlling the component. The first control units are connected to a valve control unit located on low potential level by light conductors. The light conductors carry signals associated with a change of the conducting state of the respective semiconductor component between the valve control unit and the respective first control unit, while separating them galvanically.
The above mentioned "signals associated with a change of the conducting state of the respective semiconductor component" encompasses all types of signals that may be sent between the valve control unit and the first control units in connection with a change in the conducting state of the respective semiconductor components. In the case of thyristors, this includes firing or indication signals sent in connection with turning a thyristor on, and for semiconductor components in the form of IGBT's, it is firing signals and indication signals sent in connection with turning off or short-circuiting.
Such high voltage converter stations may, for example, be stations in plants for transmitting electric power through High Voltage Direct Current (HVDC) for converting the direct voltage into alternating voltage and conversely. However, the invention is not restricted thereto, but is directed to all types of high voltage converter stations. High voltage here typically means voltages within the range of 10-500 kV. Each valve unit usually has a plurality of semiconductor components of turn-on type connected in series, such as thyristors, IGBT's or the like, which are controlled simultaneously so that they act as a single switch. The voltage to be held by the valve unit in a turned-off state of the semiconductor components is distributed among the semiconductor components connected in series, since each can normally only hold 1-5 kV.
Although it is described below that the valves have first control units, the invention also comprises the case of a directly light controlled turning-on of the semiconductor components in which the first control units then principally only conducts light pulses on the semiconductor component in question.
In the known devices in high voltage converter stations described in the introduction, two light conductors, extending between the valve control unit and the respective first control unit, are used only for communication between the electronic components on a low potential level and the individual semiconductor components, such as thyristors and IGBT's, for turning on and possibly re-turning on of thyristors and "turning on" and short circuit indication, respectively, of the IGBT's. There is no additional communication between the low potential level and the valve located on a high voltage potential level of the high voltage converter stations.
However, it is desired to extend the communication between the high voltage potential level and the low potential level in the valves, but such communication is complicated as a consequence of the high potential level on which the valve is located. The more knowledge that is available about the state of the valve, the greater will be the possibility of keeping down the high costs caused by a shut down of parts of a high voltage converter station, or the entire station during a certain period of time.